Title: Convective and Turbulent Motions in Nonprecipitating Cu. Part II: LES Simulated Cloud Represented by a Starting Plume

Abstract

The dynamic structure of a small trade wind cumulus (Cu) is analyzed using a novel approach. Cu developing in a shear-free environment is simulated by 10-m-resolution LES model with spectral bin microphysics. The aim is to clarify the dynamical nature of cloud updraft zone (CUZ) including entrainment and mixing in growing Cu. The validity of concept stating that a cloud at developing state can be represented by a parcel or a jet is tested. To investigate dynamical entrainment in CUZ performed by motions with scales larger than the turbulence scales, the modeled fields of air velocity were filtered by wavelet filter that separated convective motions from turbulent ones. Two types of objects in developing cloud were investigated: small volume ascending at maximal velocity (point parcel) and CUZ. It was found that the point parcel representing the upper part of cloud core is adiabatic. The motion of the air in this parcel ascending from cloud base determines cloud-top height. The top-hat (i.e., averaged) values of updraft velocity and adiabatic fraction in CUZ are substantially lower than those in the point parcel. Evaluation of the terms in the dynamical equation typically used in 1D cloud parcel models show that this equation canmore » be applied for calculation of vertical velocities at the developing stage of small Cu, at least up to the heights of the inversion layer. Dynamically, the CUZ of developing cloud resembles the starting plume with the tail of nonstationary jet. Both the top-hat vertical velocity and buoyancy acceleration linearly increase with the height, at least up to the inversion layer. An important finding is that lateral entrainment of convective (nonturbulent) nature has a little effect on the top-hat CUZ velocity and cannot explain the vertical changes of conservative variables qt and θl. In contrast, entrained air lifting inside CUZ substantially decreases top-hat liquid water content and its adiabatic fraction. Possible reasons of these effects are discussed.« less

Authors:

Pinsky, Mark ^[1]; Eytan, Eshkol ^[2]; Koren, Ilan ^[2]; Khain, Alexander ^[1]

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+ Show Author Affiliations

1. Hebrew Univ. of Jerusalem (Israel)
2. Weizmann Institute of Science, Rehovot (Israel)

Publication Date:

Tue Mar 01 00:00:00 EST 2022

Research Org.:

Univ. of Oklahoma, Norman, OK (United States)

Sponsoring Org.:

USDOE Office of Science (SC); European Research Council (ERC); Israel Science Foundation

OSTI Identifier:

1980919

Grant/Contract Number:  

SC0014295; 810370; 2027/17; 2635/20

Resource Type:

Accepted Manuscript

Journal Name:

Journal of the Atmospheric Sciences

Additional Journal Information:

Journal Volume: 79; Journal Issue: 3; Journal ID: ISSN 0022-4928

Publisher:

American Meteorological Society

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; Meteorology & Atmospheric Sciences; Cumulus clouds; Mixing; Convective parameterization; Large eddy simulations